Thursday, May 11, 2017

11 May 17

The lines and squiggles on my Snail Garden tie (by Jerry Garcia) today honor the birthday in 1918 of master physicist Richard Feynman. His notation for subatomic particle interactions, known as a Feynman diagram, gives a pictorial description of the complicated mathematical operations at work. I'm including a typical Feynman diagram in the photos for today. The patterns of the lines and squiggles can be enjoyed simply for their beauty. But in technical terms -- are you sure you are ready for this? -- a Feynman diagram is a graphical representation of a perturbative contribution to the transition amplitude or correlation function of a quantum mechanical or statistical field theory. The chemist in me notices the resemblance to what we draw for chemical reactions, where the "reactants" are shown as leading to the "products." The Feynman diagram does have time coordinates, but we have to resist thinking that it says "this particle goes this direction and then this other thing happens." Unlike a chemical reaction or a bubble chamber picture, "only the sum of all the Feynman diagrams represent any given particle interaction; particles do not choose a particular diagram each time they interact.
The law of summation is in accord with the principle of superposition -- every diagram contributes to the total amplitude for the process." (From Wikipedia.) Is that enough for today? (No, I do not really know what I am talking about. I just like learning about Richard Feynman, and I like this tie!)